Introduction of Iohexol-Based Measured GFR in an Outpatient Routine Setting

Background: The current KDIGO recommendations for the treatment of CKD recommend that every nephrologist should have an option for measuring kidney function (mGFR) with an exogenous substance. Currently, only iohexol or radioactively labeled DTPA are available as exogenous substances for clearance measurements. We show the introduction into clinical routine. Methods: A total of 572 patients were evaluated in the nephrology outpatient clinic for a potential kidney function measurement between October 2023 and October 2024. First, a kidney function was carried out by determining creatinine and estimating the GFR using the CKDEpi formula (eGFR). If there were reasons for the implausibility of the creatinine measurement and the associated eGFR, e.g. malnutrition, cancer disease, heart failure, catabolic diseases or sarcopenic patients, an mGFR was also carried out using iohexol clearance measurement at 3 points in time (after 3, 4 and 5 hours). The iohexol concentration was determined in the central laboratory using a standardized CE-certified laboratory kit (Nephrolyx GmbH, Berlin, Germany) and the kidney function was calculated. Results: 572 patients were evaluated. In 119 patients there were reasons why the creatinine value was estimated rather implausible. Typical reasons were rapid weight loss during cancer therapy (n=35 patients), cardiorenal syndrome (N=45 patients) and patients with longer intensive care stays (> 28 days) (N=17 patients) and other reasons (n=21). In 119 patients, kidney function could be determined using iohexol clearance.The average deviation of eGFR from mGFR was calculated as the difference expressed in%. In the patients with cancer therapy, the eGFRshowed an overestimation over 36% on average. In patients with cardiorenal syndrome, kidney function was overestimated by an average of 31%. Renal function was overestimated by 41% in patients after prolonged intensive care stays. In all other cases renal function was overestimated by 23% Conclusion: A kidney function measurement in everyday clinical practice in an outpatient clinic is possible and useful. Renal function measurement should be performed in patients with potential implausibility for creatinine-based renal function measurement. Here, overestimation of kidney function due to the estimation is often observed and this can also result in medication dosage adjustments and reclassification of kidney disease stages.